The formation of features in metal layers has been practiced for many years, in, for example, the metal working industry, and in particular, the electronics industry. The formation of electrical circuits on dielectric substrates is of particular interest to the electronics industry, and has seen much activity. This has typically been accomplished either by directly forming a positive likeness of the desired pattern, such as by electroless deposition, or by various forms of etching or removal of material from a metal layer. Wet chemical etching utilizes aggressive chemicals to dissolve unwanted portions of metal, and is the most well known and widely used method of etching. This method has the drawbacks of generating hazardous waste and limited throughput. Dry etching utilizes plasma gases or reactive ion etching to remove the metal, but requires large capital expenditures and is essentially limited to very thin layers of metal. Mechanical methods such as cutting, machining, or drilling are slow and not amenable to very small feature sizes. Lasers have also been used to cut away excess metal, and even to ablate metal away, but, again, are limited in the amount of throughput and have high capital requirements. The most popular method today in the electronics industry is the wet etching method, which uses a patterned mask of photoresist to control where underlying material is etched away and where it is left in place. Such methods provide the required degree of precision for etching semiconductor features with critical dimensions in the submicron range, but typically achieve etch rates in the range of about 1 micron or less of thickness per minute. Where the required features are relatively large scale, in the range of from about 10 to about 100 microns, or where the amount of material to be removed is large, the etch rates achievable by such methods are generally too low to be practical in commercial production. What is needed is a method for removal of metal with high precision, at etch rates exceeding any of the present technologies, that does not generate large amounts of hazardous waste.
Skilled artisans will appreciate that elements in the figures are illustrated for simplicity and clarity and have not necessarily been drawn to scale. For example, the dimensions of some of the elements in the figures may be exaggerated relative to other elements to help to improve understanding of embodiments of the present invention.